Possible reasons for the δ 13 C anomaly of Lower Proterozoic sedimentary carbonates

• Published in: Terra Nova
• Main Authors: Tikhomirova, M., Makarikhin, V.V.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1993
• Subjects: karelia*
• Online Access: http://dx.doi.org/10.1111/j.1365-3121.1993.tb00255.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-3121.1993.tb00255.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3121.1993.tb00255.x

Detailed isotopic study (δ 13 C, δ 18 O) of Lower Proterozoic sedimentary carbonates from biostratigraphically dated successions in Karelia (Russia) revealed a large positive δ 13 C anomaly (average δ 13 C‐value constitutes approximately +10‰ PDB) at 2.3 Byr ago and a huge drop of δ 13 C‐values in the subsequent ‘black shale period’(2.2 Byr ago). These data are interpreted to be a result of large‐scale changes in the oxygen content of the atmosphere. According to this model the positive carbon isotopic anomaly of sedimentary carbonates at about 2.3 Byr ago reflects a very high O 2 ‐content of the atmosphere at this time; the subsequent drop in δ 13 C‐values equates with a sharp decrease of the O 2 ‐content of the atmosphere.